1. Set 结构

[...new Set(arr)]

2. reduce

arr.reduce((pre, item, index) => {

  if(!pre.includes(item)) {
    pre.push(item)
  }
return pre

}, [])

3. filter

let arr = [1, 1, 2, 3, 4, 5, 4]
let newArr = arr.filter((item, index) => {
   return index === arr[item]
})

4. forEach 新创建一个数组

let arr = [1, 1, 2, 3, 4, 5, 4]
let newArr = []
arr.filter((item, index) => {
   if(!newArr.includes(item)) {
      newArr.push(item)
   }
})